Electrical bushing assembly having a direct cable to conductor rod terminal assembly

ABSTRACT

Bushing apparatus including a terminal assembly suitable for use with large currents. The terminal assembly clamps an electrical cable directly to the conductor rod of the bushing. The conductor rod extends through an opening in the terminal assembly with the end of the conductor rod positioned flush with the inside of the terminal assembly. Current flowing from the cable to the conductor rod does not appreciably flow through the terminal assembly.

Jan. 1, 1974 United States Patent [191 Horton, III

2,370,288 2/1945 Brolinson.................... 174/152 R X ELECTRICALBUSHING ASSEMBLY FOREIGN PATENTS OR APPLICATIONS mmm nl. m W Mn m 0a mmm0 CGL 306 566 999 mmw 563 8002 O OQ 425 223 HAVING A DIRECT CABLE TOCONDUCTOR ROD TERMINAL ASSEMBLY [75] Inventor: William E. Horton, III,Bogart, Ga.

783,796 4/1935 France.............................. 174/75 R PrimaryExaminer-Laramie E. Askin Att0rney-A. T. Stratton et a].

[22] Filed:

n -Se- H... C Hm w m m xn mn .WIa Xflt bflc w u u m edyuuw eiho w fim fbfl aro m m i o u a t n ne ma m m wm T r wnmn C mmhdw fm. A wh efi mw Rrbht Tmmw e m e m s A cw mmm nr. n. ml atsg a S Un n hh u te m 3 6 r.MmWn D- e atomw wmm mm m m hlhtt .mmmm m lh w 7 S] d 5 [Babttes R MD R 22 2 522 7%7 ,7W 2 22 b 991R0 3 25 3 5 3 H7 3 m6 W R2 n 4 R 9 3 ./33 34.,6 "NR 5 u a .3 M UN "14 4 mm m mm "m C m m m.U4 r a m wu mSl 1.. n CG M7l 2 m U hr. 2 N 5 55 [5 References Ci the cable to the conductor roddoes not appreciably UNITED STATES PATENTS flow through the terminalassembly.

498,407 5/1893 Rich.............. 339/272 A X 1 Claim, 3 Drawing FiguresELECTRICAL BUSHING ASSEMBLY HAVING A DIRECT CABLE TO CONDUCTOR RODTERMINAL ASSEMBLY BACKGROUND OF THE INVENTION l. Field of the InventionThis invention relates, in general, to electrical bushing assembliesand, more specifically, to connector terminals for electrical bushingassemblies.

2. Description of the Prior Art Connector terminals are mounted on topof electrical bushings to provide means for connecting an electricalcable to the bushing. Generally, the terminal conducts current from thecable to a conductor rod or lead which extends through the bushing. Toprevent possible destructive power losses in the connector terminal, theresistance of the portion of the connector terminal through which thecurrent passes must be low enough to safely carry the rated current. I

Connector terminals also provide a fixture in which the electrical cableis suitably clamped into position. Tosatisfactorily provide thisfunction, the connector terminal must be constructed of a materialhaving mechanical properties suitable to provide sufficient rigidity tothe connector terminal when the cable is clamped. Copper is generallyused as the material for the conductor rod. An alloy of copper isgenerally used as the material for the connector terminal to enhance themechanical properties thereof.

Typical copper alloys have a conductivity of approximately 20 percentthat of pure copper. In some applications, the difference in resistanceof the conductor rod and the connector terminal does not presentsignificant problems. Heat sink effects and design safety factors havepermitted the use of conventional connector terminals in bushings formoderately rated apparatus, such as distribution transformers. However,when the rating of the transformer becomes relatively large, such as 500KVA at 2,400 volts, conventional connector terminals are unsatisfactory.At the large power ratings, the portion of the connector terminal whichconducts the current disintegrates upon the application of power. Duringshort circuit conditions when the current is approximately 30 times therated current, de struction occurs within a few 'cycles after beingenergized, thus heat sink effects are not effective in protecting theconnector terminal from overheating.

Therefore, it is desirable, and it is a first object of this invention,to provide an electrical bushing assembly wherein the connector terminalthereof does not present a region of relatively high resistance in thepath of the current flowing through the bushing. It is also desirable,and it is a second object of this invention, to provide a connectorterminal which provides the first objective without decreasing themechanical strength of the connector terminal.

SUMMARY OF THE INVENTION There is disclosed herein new and usefulelectrical bushing apparatus suitable for use at high current levels.The bushing includes an insulator with an opening extendingtherethrough. A conductor rod is positioned within the insulator openingand is attached to a terminal assembly. The terminal assembly isconstructed with anopening through its lower portion. The conductor rodextends through the opening in the terminal assembly with the end of theconductor rod positioned in flush relationship with the inside of theterminal assembly. An electrical cable is forced against the end of theconductor rod by a shoe member attached to a rotatable threaded shaft.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of thisinvention will be come more apparent when considered in view of thefollowinging detailed description and drawing FIG. 1 is an elevationalview of an electrical bushing assembly constructed according to thisinvention with a portion thereof enlarged for clarity;

FIG. 2 is a view of the enlarged portion of FIG. 1 constructed accordingto a prior art arrangement; and

FIG. 3 is a perspective view showing components of the bushing assemblyof FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the followingdescription, similar reference characters refer to similar members inall the figures of the drawing.

Referring now to the drawing, and FIG. 1 in particu lar, there is shownan elevational view of an electrical bushing assembly constructedaccording to this invention with a portion thereof enlarged for clarity.The bushing assembly includes an insulator 1 which is constructed of aninsulating material and which contains a substantially longitudinalopening 12 extending therethrough. The sealing plug 14 is constructed ofa rubber material and is compressed within the opening 12. The insulatorincludes the shoulder region 16 which seats on the mounting surface 18,such as a transformer enclosure, with a sealing gasket 20 positionedtherebetween. Bushing retaining or fastening means for securing thebushing to the surface 18 is not illustrated.

A longitudinal conductor rod 22 is positionedin the opening 12 and isconstructed of a good electrical conducting material, such as copper.The first end of the conductor rod 22 is attached to the terminalassembly 24. The second end 25 of the conductor rod 22 provides meansfor connecting the rod 22 to the associated electrical circuitcomponents, either directly or through protective devices such as aprotective link.

The cap 26 is attached to the terminal assembly 24 and is formed aroundthe flared projection 28 of the insulator 10. A method of forming thecap 26 is disclosed in US. Pat. No. 3,258,523 which is assigned to thesame assignee as is this invention. The terminal assembly 24 alsoincludes a knob 30, a threaded shaft 32 which may be rotated by the knob30, and a shoe 34 which is attached to the lower end of the shaft 32.The shaft 32 extends through a threaded opening 36 in the terminalassembly 24 and moves the shoe 34 down against the electrical cable 38when the knob is rotated. Thus, the cable 38 may be forced against thebase portion 40 of the terminal assembly 24. A projection 42 from theterminal assembly 24 provides a lightning gap with the grounded rod 44.The terminal assembly 24 is constructed of a suitable material, such asan alloy of copper having a conductivity approximately equal to 20percent that of pure copper.

The enlarged portion of FIG. 1 shows the connection of the terminalassembly 24 to the conductor rod 22 in greater detail. The base portion40 of the terminal assembly 24 has an upper surface 46 and a lowersurface 48. A threaded opening 50 extends through the base portion 40.The lower surface 48 is secured to the cap 26 by suitable means, such asby the brazing material 52.

The region 54 of the conductor rod 22 which is located adjacent to thefirst end 56 of the conductor rod 22 is threaded to permit insertioninto the opening 50. The conductor rod 22 is positioned with its firstend 56 substantially flush with the upper surface 46. This permitscurrent flowing from the cable 38 to enter the conductor rod 22 directlywithout requiring the conduction of substantial current through the baseportion 40 of the terminal assembly 24. Suitable means, such as thebrazing material 58, may be used to provide a secure fit between theterminal assembly 24 and the conductor rod 22.

FIG. 2 illustrates the circled portion shown in FIG. 1 as it would beconstructed according to the prior art. The terminal assembly 60includes a lower projection 62 which contains a threaded opening 64. Thethreaded portion 55 of the conductor rod 22 is positioned within theopening 64. Current flowing from the cable 38 must pass through thewalls of the projection 62 to the conductor rod 22. Since theresistivity of the material comprising the projection 62 must beapproximately five times as much as that of the conductor rod 22 toprovide a mechanically rigid terminal assembly 60, excessive heat isgenerated in the projection 62 unless the cross-sectional area thereofis increased.

FIG. 3 is an exploded view showing several components of a bushingassembly constructed according to this invention. The lip 66 of thelower surface 48 extends through the opening 68 in the cap 26. Brazingmaterial may be conveniently applied by placing a washer formed frombrazing material around the lip 66 prior to insertion of the conductorrod 22.

The novel bushing assembly taught by this invention permits the use of aterminal assembly which does not have a relatively large lowerprojection for connection to a conductor rod. This permits the use ofstandard components in bushings suitable for high current ratingsr Sincenumerous changes may be made in the above described apparatus anddifferent embodiments of the invention may be made without departingfrom the spirit thereof, it is intended that all of the matter containedin the foregoing description or shown in the accompanying drawings shallbe interpreted as illustrative rather than limiting.

I claim:

1. An electrical bushing assembly comprising an insulator having asubstantially longitudinal opening therethrough and a flared projectionthereon, terminal means constructed of a first electrically conductivematerial and having a base portion with an opening extending from anupper surface to a lower surface of said base portion, a cap brazed tosaid lower surface, said cap being formed around said flared projection,a longitudinal conductor rod having first and second ends andconstructed of a second electrically conductive material, said conductorrod being positioned in the opening through said insulator with thefirst end of said conductor rod extending into the opening in andconnected to said base portion, with the first end of said conductor rodsubstantially flush with said upper surface, and means attached to saidterminal means for forcing an electrical cable against the first end ofsaid conductor rod, said first conductive material having a lowerconductivity and greater mechanical strength than said second conductivematerial.

1. An electrical bushing assembly comprising an insulator having asubstantially longitudinal opening therethrough and a flared projectionthereon, terminal means constructed of a first electrically conductivematerial and having a base portion with an opening extending from anupper surface to a lower surface of said base portion, a cap brazed tosaid lower surface, said cap being formed around said flared projection,a longitudinal conductor rod having first and second ends andconstructed of a second electrically conductive material, said conductorrod being positioned in the opening through said insulator with thefirst end of said conductor rod extending into the opening in andconnected to said base portion, with the first end of said conductor rodsubstantially flush with said upper surface, and means attached to saidterminal means for forcing an electrical cable against the first end ofsaid conductor rod, said first conductive material having a lowerconductivity and greater mechanical strength than said second conductivematerial.